Video compression is the process of taking a video signal and compressing it so that it will take up less bandwidth when it is transmitted or less space when it is stored. Many video compression standards have been developed and include H.262, H.263, MPEG-1, MPEG-2, and MPEG-4. Many of these standards separate video into blocks of data and separately compress each block using a Discrete Cosine Transform (DCT). One problem with these compression algorithms, however, is that video that undergoes such compression may be subject to “blockiness”, meaning that the block and macroblock structure of the picture is visible.
A blockiness measurement is a quantification of the blockiness of the decompressed video image. The blockiness measurement can be used to determine the quality of the compressed video signal since blockiness is a severe compression artifact. The blockiness artifact is especially apparent at low bit rates and when the compressed signal has been corrupted. At low video bit rates over-compression would cause visible block transitions in smooth textual areas, such as sky, grass, or the shade of a wall. At low or high video bit rates, corruption of a compressed signal would cause visible foreign blocks in the picture.
Ideally the amount of compression is maximized while still providing a video image or picture that is free of artifacts such as blockiness. Accordingly there is a need for a real-time blockiness detection system which can be used to decrease the level of compression if the blockiness reaches a certain threshold or increase the level of compression if the blockiness falls below a certain threshold.